The proposed studies will expand upon my preliminary work on neuronal RNA content, dendritic ramification, and synaptic density in the prefrontal cortex of rhesus monkeys ranging from 7 to 28 years of age. Dendritic branching patterns and synaptic density of the subiculum will be quantitated by using the rapid Golgi method for light microscopy and the phosphotungstic acid staining method for electron microscopy. Morphometric measurement of these neuronal parameters will be obtained with the use of the computerized digitizer. The studies will then examine the possibility that changes in the dendritic ramification and synaptic density may reflect aging changes in the rhesus monkey brain. This data obtained on the rhesus monkey will be important in relating present knowlege of the aging brain in other species to the aging human brain.